Third generation partnership project (3GPP) and Long Term Evolution (LTE) mobile telecommunication systems provide high data rate, lower latency and improved system performances. With the rapid development of “Internet of Things” (IOT) and other new user equipment (UE), the demand for supporting machine communications increases exponentially. To meet the demand of this exponential increase in communications, additional spectrum (i.e. radio frequency spectrum) is needed. The amount of licensed spectrum is limited. Therefore, communications providers need to look to unlicensed spectrum to meet the exponential increase in communication demand. One suggested solution is to use a combination of licensed spectrum and unlicensed spectrum. This solution is referred to as “Licensed Assisted Access” or “LAA”. In such a solution, an established communication protocol such as Long Term Evolution (LTE) can be used over the licensed spectrum to provide a first communication link, and LTE can also be used over the unlicensed spectrum to provide a second communication link.
Furthermore, while LAA only utilizes the unlicensed spectrum to boost downlink through a process of carrier aggregation, enhanced LAA (eLAA) allows uplink streams to take advantage of the 5 GHz unlicensed band as well. Although eLAA is straightforward in theory, practical usage of eLAA while complying with various government regulations regarding the usage of unlicensed spectrum is not so straightforward. Moreover, maintaining reliable communication over a secondary unlicensed link requires improved techniques.
In 3GPP Long-Term Evolution (LTE) networks, an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of base stations, e.g., evolved Node-Bs (eNBs) communicating with a plurality of mobile stations referred as user equipment (UEs). Orthogonal Frequency Division Multiple Access (OFDMA) has been selected for LTE downlink (DL) radio access scheme due to its robustness to multipath fading, higher spectral efficiency, and bandwidth scalability. Multiple access in the downlink is achieved by assigning different sub-bands (i.e., groups of subcarriers, denoted as resource blocks (RBs)) of the system bandwidth to individual users based on their existing channel condition. In LTE networks, Physical Downlink Control Channel (PDCCH) is used for downlink scheduling. Physical Downlink Shared Channel (PDSCH) is used for downlink data. Similarly, Physical Uplink Control Channel (PUCCH) is used for carrying uplink control information. Physical Uplink Shared Channel (PUSCH) is used for uplink data.
In Rel-14 LAA, uplink grants for a UE in a subframe can enable PUSCH transmission for the UE in multiple subframes for both cross-CC scheduling case and self-scheduling case. For UL transmission in eLAA, flexible timing between the subframe carrying the UL grant and subframes of the corresponding PUSCHs is supported. For the details of UL grant(s) for a UE in a subframe enabling PUSCH transmission for the UE in multiple subframes in LAA, at least the following options are considered. Option 1) Single UL grant in a subframe for a UE can schedule N (N≥1) PUSCH transmissions for the UE in N subframes with single PUSCH per subframe. Option 2) Single UL grant in a subframe for a UE can schedule single PUSCH transmission in a single subframe while UE can receive multiple UL grants in a subframe for PUSCH transmissions in different subframes. Option 3) Single UL grant in a subframe for a UE can enable the UE to transmit single PUSCH transmission among one of the multiple subframes depending on UL LBT result.
The support of Hybrid Automatic Retransmission (HARQ) is an important feature in eLAA. HARQ allows a link to be operated with a tradeoff between throughput and latency as determined by the serving base station. A flexible and efficient PDCCH signaling scheme that schedules PUSCH transmission over multiple subframes with HARQ support is sought.